All-time low in Florida, numbers receding (5)
I believe the answer is:
Here is my best explanation:
'all-time low' is the definition.
(I've seen this before)
'in florida numbers receding' is the subsidiary indication.
'in' indicates a hidden word.
'receding' says the letters should be written in reverse.
'ridan' is hidden within 'florida numbers'.
'ridan' backwards is 'nadir'.
(Other definitions for nadir that I've seen before include "Low point", "Drain (anag)", "Low-water mark", "Deepest point", "Floor of drain in need of repair", "It's opposite the zenith", "The lowest point of anything", "Bottom", "Lowest point, or time of deepest depression." and "Drain to lowest level".)